The present invention pertains generally to infrared oscillators and amplifiers and more particularly to stimulated Raman scattering utilizing rotational transitions in a diatomic molecular gas.
Various methods have been disclosed for shifting frequencies of conventional lasers in the IR spectrum. These methods have included four-wave mixing as disclosed in application Ser. No. 787,415 filed Apr. 14, 1977 by Richard F. Begley et al. entitled "Resonantly Enhanced Four-Wave Mixing" now U.S. Pat. No. 4,095,121 and Raman scattering, as disclosed in application Ser. No. 466,583 filed May 2, 1974 by C. D. Cantrell et al. entitled "Infrared Laser System now U.S. Pat. No. 4,061,921. In each of these systems and other previous systems for IR frequency shifting to a broad range of frequencies, simplicity and overall efficiency are important factors for economic utilization of the device. By minimizing the steps required for frequency shifting, such as elimination of the Raman spin-flip laser, as set forth in the above disclosed application Ser. No. 466,583, the device can be simplified to reduce problems inherent in more complex systems.
Since the stimulated Raman effect can be produced in a single step with high conversion efficiency, Raman shifting of CO.sub.2 laser radiation provides high overall efficiencies due to the high efficiencies and well developed technology of CO.sub.2 lasers. However, Raman gain in gaseous media such as H.sub.2, D.sub.2, HD, HT, DT or T.sub.2 requires powers which are near the breakdown threshold of these diatomic molecular gases for a single pass focused geometry, such as suggested by Robert L. Byer, in an article entitled "A 16 .mu.m Source for Laser Isotope Enrichment" published in IEEE Journal of Quantum Electronics, Vol. QE12, pp. 732-733, November 1976.
Other devices have also used rotational Raman gain to generate Stokes signals such as disclosed in copending application Ser. No. 802,400 entitled "Shifting of CO.sub.2 Laser Radiation Using Rotational Raman Resonances" filed June 1, 1977 by Norman A. Kurnit, of which the present invention comprises an improvement. The device of the above disclosed invention relies upon spontaneous generation of the desired Stokes signal. Such a system, of course, requires high power densities and long focal interaction lengths to ensure spontaneous generation of the desired Stokes signal.